In wireless communication systems, it is difficult to transmit data since various types of errors are generated due to propagation of transmitted signals in a wireless manner. In addition to thermal noise represented as additive white Gaussian noise (AWGN), path loss that increases with increasing distance from an eNode B (eNB), multi-path fading, etc. generated in radio channels make reliable signal transmission difficult.
To secure transmission reliability against generation of various channel state variations and errors in wireless communication, technologies such as 1) forward error correction (FEC) or channel coding and 2) automatic repeat request (ARQ) or hybrid automatic repeat request (HARQ) are widely used.
In a next-generation 3GPP LTE-A communication system, two types of links having different attributes are respectively applied to uplink and downlink carrier frequency bands as a relay forwards link connection between en eNB and a user equipment (UE). Connection link established between the eNB and the relay is defined as a backhaul link. The relay can receive information from the eNB through a relay backhaul downlink and transmit information to the eNB through a relay backhaul uplink. Furthermore, the relay can transmit information to the UE through a relay access downlink and receive information from the UE through a relay access uplink.
For the 3GPP LTE-A system to which the relay has been introduced, there is not provided a HARQ process performed between the relay and the eNB and between the eNB and the UE, for example, a method of determining the number of HARQ processes, information about a subframe to which a HARQ process is applied, etc. Accordingly, a HARQ process taking introduction of a relay into account is needed.